As is well known, the quantity of waste and/or recycled materials, and in particular, plastics, rubber and other material having a relatively high molecular weight and a significant content of hydrocarbon-forming materials, have been increasing continuously for many years, disposal of waste plastics in landfills and similar repositories is highly unsatisfactory for a number of reasons, and methods of recycling waste plastics and other such materials have consistently met with and failed to overcome the serious economic, practical and technical difficulties inherent therein. There is no end in sight to the increase in quantity of such materials used by humans. Landfill disposal has long been recognized as problematic and quite unsatisfactory for reasons including the extensive time required for most polymers to degrade, the loss of resources represented by the millions of tons of polymeric materials which are discarded every year, and the danger inherent in the eventual decomposition of these materials. A great variety of methods of recycling plastics have been developed and most have been discarded as economically non-viable. The reasons for this include the difficulty in identifying, sorting and separating the many different types of plastics, blending in other materials, the difficulty in developing functional continuous processes and equipment for recycle of those relatively few types of plastics that actually lend themselves to reuse, the difficulty in developing systems for the pyrolytic (or other) degradation of the many different types of plastics into hydrocarbon products, and the difficulty in dealing with the remaining byproducts from such pyrolytic processes.
One reason prior art processes have failed to be economically viable, particularly in regard to the amount of hydrocarbon materials recovered relative to the cost of operating the process, is that plastic materials have a very low thermal conductivity. The low thermal conductivity can lead to low through-put relative to the size of equipment and quantity of energy expended in attempting to convert the feed materials into hydrocarbons. Due to inefficient use of the applied heat, the prior art has employed large and complicated conventional heat transfer apparatus, especially in the initial heating stages. For example, the peripherally heated stirred pot concept is of limited utility and quite low efficiency due to the poor heat transfer through the large mass of material sought to be heated. In prior art processes, these factors have resulted both in an unacceptably low return on investment due to inefficient operation resulting from the poor heat transfer and in the formation of relatively large quantities of carbonaceous char and low value non-condensable byproducts, further reducing the quantity of valuable, useable hydrocarbon products obtained from these processes.
For at least these reasons, an unmet need remains for a fast, efficient, relatively small and simple system and process for receiving, pyrolyzing and recovering useful hydrocarbon products from waste plastics in an economically efficient manner, relatively free of technical difficulties arising from the very nature of the raw materials fed into the system and process.